

//结果
type testw1 = {
  age?: number | undefined
}

/* Exclude */
type testa = Exclude<'a' | 'b' | 'c', 'a' | 'b'>

//原理 extends一个约束
type CustomExclude<T, K> = T extends K ? never : T
//结果
type testa1 = 'c'
